1) calculate total energy to needed to melt ice
2) calculate energy per photon
3) calculate number of photons...
Thank you for the reply.
But 1) is wrong. The correct calculation is to use Einstein's mass-energy equation: E = mc^2. The m in the equation refers to the mass of a molecule of water, c is speed of light and E is the total energy of the molecule.
Since your premise 1) is not correct, you got an erroneous result of the calculation.
I haven't found the data about the mass of a molecule of water.